JPH08206636A - Regeneration of contaminated wet soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the extraction of a contaminant from soil by improving the contact of soil with an extractant by using an extractant having high solvent capacity to a contaminant and adding a very small amt. of a hydrophilic co- solvent to the extractant. SOLUTION: A high b.p. org. contaminant is separated from a compsn. constituted of water of an amt. from 5% to the threshold value of soil water capacity and soil containing the high b.p. org. contaminant. At this time, the compsn. is brought into contact with an extractant mixture consisting of a solvent for fractionating petroleum and a polar co-solvent which are selected so as to be capable of constituting a single liquid phase along with water contained in the compsn. to be mutually mixed. Next, a coarse fraction of soil is separated from a liquid phase containing a fine fraction of soil and, subsequently, the liquid phase is separated from the fine soil fraction. The coarse and fine soil fractions are dried. The contaminant is a polynuclear aromatic substance or an organochlorine compd. and, as the solvent, ethyl acetate is designated and, as the co-solvent, acetone and acetic acid are designated.

Description

Detailed Description of the Invention

The present invention relates to a method of treating wet soil contaminated with high-boiling organic substances using a mixture of hydrophobic and hydrophilic solvents. The problem of soils contaminated with high-boiling organic pollutants such as hydrocarbons, polynuclear aromatics and organochlorines is not only related to actions to be taken against soil and groundwater contamination in industrialized countries, However, the need to regenerate the ground surface for industrial and residential use is also becoming increasingly important. Another serious problem typical of the oil sector is the disposal of drilling waste before it is dumped into the sea. In Italy, about 1 per year
The 4,000 m ³ of oil-contaminated waste from offshore drilling sites must be treated. The mode of pollution as well as the nature of the polluted soil are very different. Under these circumstances, a wide range of solutions and actions are needed.

Widely used is the technique of "soil cleaning," which is a technique that only uses water, optionally with additives. Unfortunately this technology
There is a drawback that a large amount of extractant is used and it is generally difficult to recover the additive (surfactant). Other methods that rely on the use of solvents have also been used. Among these methods,
Liquefied C ₂ -C ₄ hydrocarbons, supercritical fluids, methylene chloride,
Mention may be made of a number of patents claiming the use of etc. However, contaminated soil containing a large amount of H ₂ O (> 5% by weight) is difficult to treat with solvent extraction technology for the following reasons. Contaminants are generally non-polar or less polar, aliphatic hydrocarbons, polynuclear aromatic hydrocarbons, organochlorines, etc., so that the most suitable solvent for such pollutants. Is a less polar or non-polar solvent. Furthermore, effective extraction of pollutants from soil requires that the soil to be regenerated be in intimate contact with the extractant. It is difficult to achieve this condition when using non-polar solvents, wet soil (H ₂ O> 5%)
Mixes readily with polar solvents only.

We hereby solve these problems by using an extractant with a high solvent capacity for pollutants and improving the contact of the soil with the extractant by adding very small amounts of hydrophilic cosolvents. It was solved by the method of treating contaminated soil.
Therefore, the present invention is a method for separating a high-boiling organic pollutant from a composition composed of soil containing 5% to a threshold of soil water content and a high-boiling organic pollutant. (A) The composition comprises a solvent for the petroleum fraction of the composition and a polar co-solvent, such that the solvent and co-solvent can form a single liquid phase with the water contained in the composition. And contacting with the extractant mixture, which are mixed with each other in such a proportion, (b) separating the coarse fraction of soil from the liquid phase containing the fine fraction of soil, (c) fine A method of separating a liquid phase from a soil fraction, and (d) drying the coarse soil fraction obtained in step (b) and the fine soil fraction obtained in step (c).

When choosing solvent-cosolvent pairs, they are non-toxic (however a small amount of solvent remains in the treated soil) and volatile (and therefore easily removed from the soil). Possible), inexpensive, and readily available materials should be considered. Under the preferred conditions, the solvent is ethyl acetate and the co-solvent is selected from acetone and acetic acid. The optimum solvent: cosolvent weight ratio that can be mixed with water contained in the soil to form a single liquid phase can be calculated by starting from a purpose-built phase diagram. In this way, an extractant mixture is obtained which minimizes the consumption of polar solvents and allows the extractant to contact the soil most effectively. The weight ratio of wet soil to extractant mixture can be varied within a range, but under preferred conditions such ratio is 1: 1.
Is. Moreover, if necessary, the extraction step (a) can be repeatedly performed. The separation according to (b) and (c) can be carried out by sieving or using a wet cyclone, but if only small amounts are to be processed, centrifugation can also be used. The drying step (d) can be carried out by a dryer or desiccator, a spray dryer or other technique known from the prior art. By this method, the use of a hydrophilic / hydrophobic solvent system with a suitable composition can give better results than possible with a single-component system, the "history" of pollution, that is to say of the soil, for example. Regardless of whether the pollution occurred before or after the rain.

The following examples are intended to illustrate the invention in more detail and not to limit it. Examples 1-5 Ethyl acetate (solvent), composed of acetone (cosolvent) and water systems, which can be represented by the ternary phase diagram (isothermal) shown in FIG. 1, the solvent and H ₂ O portion of the therein Immiscible regions are present because they are mutually miscible. A system having a composition falling inside the immiscible region spontaneously undergoes phase separation and
Systems that form two phases and, on the contrary, whose composition lies outside the immiscible region, constitute a single phase. H ₂ O contained in soil
Soil can be considered as free water, soil: extractant = 1:
The minimum content of acetone to be added to the ethyl acetate to obtain a single phase while maintaining the ratio of 1 is determined by finding the threshold composition of the immiscible region from the triangular figure (hereinafter Called "system percentage"). To select the solvent mixture, it is not necessary to consider the type of soil, sandy or muddy, it is sufficient to know the water content of the soil. Table 1
For various moisture percentages in soil, and 1: 1
The appropriate ethyl acetate: acetone mixture is shown for the soil: extractant ratio (S / E). A plurality of samples of sandy soil to be reclaimed, each with a total weight of 100 g, are operated and produced in the laboratory according to the following procedure.

89 g of pre-dried sandy soil was added with H ₂ O.
10 g are added, the mixture is homogenized and equilibrated for about 4 hours. Then 1 g of (Arabic light) crude oil is added and the mixture is homogenized and equilibrated overnight (about 16 hours). The soil was divided into five equal samples with a water content of 10% and the following different solvent: cosolvent systems were used, with a soil: extractant ratio of 1:
1, used to perform a one-step regeneration test. 1 = Acetone 2 = Petroleum ether 3 = Ethyl acetate 4 = Ethyl acetate / Acetic acid 5 = Ethyl acetate / Acetone Separation step (b) is carried out with a vibrating sieve having a 106 micron mesh opening and separation step (c) is 700xg
By centrifugation. The solid fraction is oven dried at 105 ° C. for 2 hours. The results are shown in Table 2, where
“R” represents the removal efficiency, and the ratio of the difference between the initial contamination (Ii) and the final contamination (If) to the initial contamination is multiplied by 100. The formula is R = [(Ii-If) / Ii] × 100. "Res" represents residual soil contamination and is expressed as a percentage of dry matter obtained by extracting a portion of the regenerated sample with methylene chloride in a Soxhlet extractor. When possible, residual contaminants were applied to both soil fractions, namely coarse (> 106 micron) and fine (<106 micron) fractions, because the vibrating screen failed to separate fine fractions. In some cases, there may only be values for the coarse fraction. Such a phenomenon is
It occurs when the polar solvent is used and does not make good contact with the moist surface of the soil particles and these particles remain attached to each other (aggregation). The third line of the table gives the weight average value of the contamination of the treated samples.

Examples 6 to 10 A series of samples of sandy soil to be reclaimed, each with a total weight of 100 g, was used except that the soil was first contaminated and then moistened.
It was manufactured and operated in the laboratory by the same procedure as in Examples 1-5. The results obtained after the treatment are shown in Table 3. It should be noted that the efficiency of removal with petroleum ether varies significantly depending on the pollution mode.

Examples 11 to 15 A series of samples of muddy soil to be reclaimed, each with a total weight of 100 g, are prepared by the following procedure. (A) 74 g of pre-dried muddy soil is mixed with 25 g of H ₂ O, the mixture is homogenized and equilibrated for several hours (about 4 hours). (B) Then 1 g of (Arabic light) crude oil is added and the mixture is equilibrated overnight (about 16 hours). The results obtained after the treatment are shown in Table 4.

Examples 16 to 20 A series of samples of sandy soil to be reclaimed, each with a total weight of 100 g, was prepared by the same procedure as in Examples 11 to 15 except that the soil was first contaminated and then moistened. It was operated and manufactured in the laboratory. The results obtained after the treatment are shown in Table 5. Once again, the removal effect obtained by treatment with the mixture is independent of the history of fouling and differs from treatment with a single solvent, in particular with petroleum ether.

Example 21 A sample of sandy soil to be reclaimed is treated as follows. 94 g of pre-dried soil are mixed with a solution of 1 g of phenanthrene (polynuclear aromatic hydrocarbon) in 10 g of methylene chloride. The sample obtained is homogenized and the methylene chloride is evaporated in a circulating air oven at 50 ° C. for 3 hours.
Then 5 g of water are added and the mixture is homogenized and equilibrated overnight. The sample is repeated except that the washing step is repeated three times with fresh solvent consisting of 95: 5 ethyl acetate: acetic acid each.
Regeneration is carried out in the same manner as described in Examples 1-5. The results are shown in Table 6.

Example 22 A sample of muddy soil is treated as in Example 21. The results are shown in Table 7.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Brief description of drawings]

FIG. 1 is a ternary phase diagram of a system consisting of ethyl acetate (solvent), acetone (cosolvent) and water.

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Claims (10)

[Claims] 1. A method for separating high boiling organic pollutants from a composition composed of soil containing 5% to a threshold of soil water content and water containing high boiling organic pollutants,
(A) The composition comprises a solvent for the petroleum fraction of the composition and a polar cosolvent, such that the solvent and cosolvent can form a single liquid phase with the water contained in the composition. Contacting with the extractant mixture, selected and mixed with water contained in the composition in a proportion such that a single liquid phase can be constituted, (b) from the liquid phase containing a fine fraction of soil to the soil Separating the coarse fraction, (c) separating the liquid phase from the fine soil fraction, and (d) the coarse soil fraction obtained in step (b) and the fine soil fraction obtained in step (c). A method comprising the step of drying. 2. The method according to claim 1, wherein the pollutant is petroleum or a petroleum fraction. 3. The method according to claim 1, wherein the pollutant is a polynuclear aromatic material. 4. The method according to claim 3, wherein the polynuclear aromatic substance is phenanthrene. 5. The method according to claim 1, wherein the pollutant is an organic chlorine-based substance. 6. The method according to claim 1, wherein in the step (a), the solvent is ethyl acetate. 7. The method according to claim 1, wherein in the step (a), the cosolvent is acetone. 8. The method of claim 1, wherein in step (a) the cosolvent is acetic acid. 9. The method according to claim 1, wherein in the step (a), the weight ratio of the composition to the extractant mixture is 1: 1. 10. The method of claim 1, wherein the composition is an oil contaminated waste derived from oil drilling.